Multiple-ratio automatic transmissions for automotive vehicle drivelines have multiple-ratio gearing and fluid pressure-activated clutches and brakes that are engaged and released under the control of a hydraulic valve circuit. The circuit includes a manual valve that can be shifted linearly to each of several drive ranges for the multiple-ratio transmission. The clutches and brakes establish and disestablish each of several torque flow paths through the gearing. The circuit is supplied with fluid pressure developed by an engine-driven pump.
The control circuit includes a pressure regulator that regulates line pressure made available by the pump. Regulated line pressure is distributed to selected valve members to establish the various forward driving ratio ranges and a reverse driving ratio. The selection of the drive ranges and reverse is under the control of a manual valve. A driver-operated mechanical linkage is used to adjust the position of the manual valve.
In order to obtain an accurate indication of the actual position of the manual valve, a mechanical position sensor is located on the exterior of the transmission housing, which contains the control valve system and the multiple-ratio gearing.
The position sensor comprises a mechanical lever connected directly to the manual valve. The position of the mechanical lever is detected by a sliding electrical contact array, which forms a part of an electric sensor circuit that detects the various manual valve positions.
A position sensor of this kind has inherent disadvantages because it is susceptible to malfunction if the sliding contacts of the contact array become contaminated and establish an open circuit in the position sensor. The sensor also creates driveline packaging difficulties because of the space that must be dedicated to the sensor.